Canine Appendicular Osteosarcoma
What is appendicular osteosarcoma?
Takeaways
- Appendicular osteosarcoma is a common bone tumor dogs.
- It most commonly affects large breed dogs.
- It is associated with a high rate of tumor spread (metastasis), often to the lungs.
- Treatment usually requires surgery to remove the tumor. This may involve amputation of the affected limb or limb-salvage surgery, followed by chemotherapy.
- In most cases, the tumors arise spontaneously, with no identified cause.
Osteosarcoma is a common, aggressive and invasive bone tumor in dogs. Breeds at increased risk of developing osteosarcoma include Doberman Pinschers, German Shepherds, Golden Retrievers, Great Danes, Irish Setters, Rottweilers and Saint Bernards. Although it is most often diagnosed in older (7 to 10 years of age), large or giant breed dogs, it can affect dogs of any size, breed or age. Osteosarcoma can be found in many areas of the body, but it most commonly appears in regions of the appendicular skeleton, the weight-bearing bones of the skeleton that support the limbs, such as those bordering the shoulder, wrist and knee. The front limbs are affected more often than the hind limbs. Tumors destroy bone locally and may spread to the lungs more rapidly than with other canine bone cancers.
What are the clinical signs of appendicular osteosarcoma?
Most dogs with appendicular osteosarcoma have a history of limb lameness that does not improve or only improves transiently with pain medications. The limb(s) may also exhibit swelling. In some cases, fractures may occur due to weakening of the bone. A hard, painful mass may be present at the affected site. If the tumor has spread (metastasized) to the lungs, generalized weakness, swelling of all four limbs, and breathing difficulties may be observed.
How we can help
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How is appendicular osteosarcoma diagnosed?
The first step in diagnosing osteosarcoma and other primary bone tumors is to take radiographs (X-rays) of the affected limb. In most cases, this can help further the diagnosis and give an idea of how certain it is that a bone tumor is present. It does not give a 100% sure diagnosis, however. A careful physical exam is also important to assess the overall health of the dog.
Radiographs will be taken of the dog's chest to see if the tumor has spread to the lungs. It is important to find out whether the cancer has spread to the lungs, as treatment options and prognosis are very different if lung metastasis has occurred. In the initial diagnostic stages, local lymph nodes and any skin masses may be aspirated, or an abdominal ultrasound may be performed.
Another diagnostic test that may be performed is a bone scan. This test, which requires an overnight stay in the hospital, will help determine whether the tumor has spread to other bones and how much of the bone where the primary tumor is located is affected. This test is common for patients who will undergo a treatment that spares the affected limb, and is not required for every patient.
To obtain a definitive diagnosis, it is necessary to aspirate the tumor with an ultrasound-guided needle or perform a bone biopsy in order to identify the type of tumor. These procedures require sedation or anesthesia. There is often a large amount of bony reaction associated with this type of tumor, so it can be difficult to obtain an adequate sample of the actual tumor cells. Additionally, only small samples are taken in order to minimize the spread of the tumor cells along the biopsy pathway and to avoid fracturing the bone. For these reasons, the biopsy procedure does not always yield a sample that is sufficient for diagnosis. Although bone biopsies are performed with the utmost care, there is always a small risk of fracturing the bone. This procedure is not performed if the exact diagnosis is not important to begin treatment.
How is appendicular osteosarcoma treated?
Treatment for canine appendicular osteosarcoma usually requires surgery to remove the tumor. This may involve amputation of the affected limb or limb-salvage surgery followed by chemotherapy.
Aside from the possibility that the cancer will spread, the tumor is painful and once it has destroyed enough of the bone, even normal activities such as walking or running can cause the bone to break. The standard treatment for an osteosarcoma is the amputation of the affected limb. Most dogs recover quite well from this procedure.
Dogs that have other orthopedic problems or are obese may not be good candidates for amputation. If this is the case, a limb sparing procedure may be performed in which the tumor is removed and the bone is replaced with another bone from the dog, a bone from a bone bank, or a prosthetic implant. The availability of this procedure depends on the location and size of the tumor. Due to the high rate of complications, amputation may eventually become necessary.
Chemotherapy is an important follow-up step in the treatment of osteosarcoma. Although there may be no clear evidence that the tumor has spread, it is estimated that over 90% of dogs with this type of tumor have microscopic spread before amputation or limb-sparing procedures are performed. Although chemotherapy has not been shown to be very effective in treating osteosarcoma when there are visible signs of spread, it is very effective in treating microscopic disease. The protocol usually requires six treatments given three weeks apart.
If amputation or limb-sparing procedures are not possible or desirable, palliative radiation therapy is an alternative approach. Although it does not generally increase a dog's survival time, it does alleviate the pain caused by the tumor in about 75% of dogs treated. Radiation therapy requires one treatment per week for four weeks, administered while the patient is under general anesthesia. Usually this is done in conjunction with other drugs to help alleviate pain.
What is the prognosis for appendicular osteosarcoma?
Chemotherapy as a follow-up treatment to amputation or limb-sparing procedures increases the median life expectancy to about one year. By two years, 10-20% of the dogs who have received chemotherapy appear to be free of cancer. Most dogs tolerate the therapy very well and experience few side effects. The median survival time with amputation alone is about three months. Cases in which the dog is diagnosed at a young age or the tumor has metastasized have poorer prognoses.
How can appendicular osteosarcoma be prevented?
In most cases, bone tumors arise spontaneously, with no identified cause.
For more information:
UC Davis School veterinary hospital Oncology Service
This article is designed to answer some of the basic questions relating to canine appendicular osteosarcoma. Your dog's particular situation may vary.
*This article may not be reproduced without the written consent of the UC Davis School of Veterinary Medicine.